ALSA: hda: Gate ELD usage only by whether ELD is valid

It's perfectly valid for an ELD to contain no SADs. This simply means that
only basic audio is supoprted.

In this case, we still want to limit a PCM's capabilities based on the ELD.

History:

* Originally, ELD application was limited solely by sad_count>0, which
  was used to check that an ELD had been read.
* Later, eld_valid was added to the conditions to satisfy.

This change removes the original sad_count>0 check, which when squashed
with the above two changes ends up replacing if (sad_count) with
if (eld_valid).

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>